A vena cava filter is a device inserted into a blood vessel to capture particles in the blood flow. Typically the device is inserted into a major vein to prevent a blood clot from reaching the lungs. Patients who have recently suffered from trauma, heart attack (myocardial infarction), or underwent major surgical procedure (e.g., surgical repair of a fractured hip, etc.) may have thrombosis in a deep vein. When the thrombus clot loosens from the site of formation and travels to the lung it may cause pulmonary embolism, a life-threatening condition. A vena cava filter may be placed in the circulatory system to intercept the thrombi and prevent them from entering the lungs.
Examples of various blood vessel filters are disclosed in U.S. Patent Application, Publication No. 2001/0000799 A1, titled “BODY VESSEL FILTER” by Wessman et al., published May 3, 2001; U.S. Patent Application, Publication No. 2002/0038097 A1, titled “ATRAUMATIC ANCHORING AND DISENGAGEMENT MECHANISM FOR PERMANENT IMPLANT DEVICE” by Ostrovsky et al., published Sep. 26, 2002; U.S. Patent Application, Publication No. 2002/0193828 A1, titled “ENDOVASCULAR FILTER” by Griffin et al., published Dec. 19, 2002; U.S. Patent Application, Publication No. 2003/0199918 A1, titled “CONVERTIBLE BLOOD CLOT FILTER” by Patel et al., published Oct. 23, 2003; U.S. Patent Application, Publication No. 2003/0208227 A1, titled “TEMPORARY VASCULAR FILTERS AND METHODS” by Thomas, published Nov. 6, 2003; U.S. Patent Application, Publication No. 2003/0208253 A1, titled “BLOOD CLOT FILTER” by Beyer et al., published Nov. 6, 2003; U.S. Pat. No. 4,425,908, titled “BLOOD CLOT FILTER” issued to Simon, dated Jan. 17, 1984; U.S. Pat. No. 4,643,184, titled “EMBOLUS TRAP” issued to Mobin-Uddin, dated Feb. 17, 1987; U.S. Pat. No. 4,817,600, titled “IMPLANTABLE FILTER” issued to Herms et al., dated Apr. 4, 1989; U.S. Pat. No. 5,059,205, titled “PERCUTANEOUS ANTI-MIGRATION VENA CAVA FILTER” issued to El-Nounou et al., dated Oct. 22, 1991; U.S. Pat. No. 5,626,605, entitled “THROMBOSIS FILTER” issued to Irie et al., dated May 6, 1997; U.S. Pat. No. 5,755,790, titled “INTRALUMINAL MEDICAL DEVICE” issued to Chevillon et al., dated May 26, 1998; U.S. Pat. No. 6,258,026 B1, titled “REMOVABLE EMBOLUS BLOOD CLOT FILTER AND FILTER DELIVERY UNIT” issued to Ravenscroft et al., dated Jul. 10, 2001; U.S. Pat. No. 6,497,709 B1, titled “METAL MEDICAL DEVICE” issued to Heath, dated Dec. 24, 2002; U.S. Pat. No. 6,506,205 B2, titled “BLOOD CLOT FILTERING SYSTEM issued to Goldberg et al., dated Jan. 14, 2003; and U.S. Pat. No. 6,517,559 B1, titled “BLOOD FILTER AND METHOD FOR TREATING VASCULAR DISEASE” issued to O'Connell, dated Feb. 11, 2003; U.S. Pat. No. 6,540,767 B1, titled “RECOILABLE THROMBOSIS FILTERING DEVICE AND METHOD” issued to Walak et al., dated Apr. 1, 2003; U.S. Pat. No. 6,620,183 B2, titled “THROMBUS FILTER WITH BREAK-AWAY ANCHOR MEMBERS” issued to DiMatteo, dated Sep. 16, 2003; each of which is incorporated herein by reference in its entirety.
Typically the filter comprises a plurality of radially expandable legs that supports one or more filter baskets which are conical in configuration. The device is adapted for compression into a small size to facilitate delivery into a vascular passageway and is subsequently expandable into contact with the inner wall of the vessel. The device may later be retrieved from the deployed site by compressing the radially expanded legs and the associated baskets back into a small size for retrieval. The radially expandable leg may further comprise engagements for anchoring the filter in position within a blood vessel (e.g., vena cava). For example, the expandable legs may have hooks that can penetrate into the vessel wall and positively prevent migration of the filter in either direction along the length of the vessel. The body of the filter may comprise various biocompatible materials including compressible spring metals and shape memory materials to allow easy expansion and compression of the filter within the vessel. The hooks on the radially expandable legs may further comprise materials more elastic than the legs to permit the hooks to straighten in response to withdrawal forces to facilitate withdrawal from the endothelium layer without risk of significant injury to the vessel wall. In one variation, the hooks are formed on the ends of a portion of the radially expandable legs, but not on others.
Many of the existing vena cava filters routinely encounter problems during deployment due to entanglements of the radially expandable legs. This is especially problematic in designs with hooks implemented on the radially expandable legs. In the compressed/collapsed condition, the various hooks on the legs may interlock with other legs or hooks and render the device useless. Thus, an improved filter design that can prevent entanglement and/or interlocking of the radially expandable legs may be desirable. Such a design may improve the reliability of the vena cava filter and improve the surgical success rate of filter implantation. Such an improved design may also prevent the entanglement of the radially expandable legs when the device is collapsed into the compressed position during the retrieval of the filter from its deployed location within the vessel.